I started getting in shape by running (crazy i know), and got so addicted to being active, that I have sense progressed to training for (and competing in) triathlons. But when I started, I read a book by Stu Mittleman called Slow Burn that is from a running perspective, but can easily be taken over into any sport. It does focus on heart rate training, but it has some real good reasons to do it, and understand it. I found an article online (http://www.rrca.org/resources/articles/slowdown.html) that gives you the meat and potatoes out of at least the heart rate part, but if you like to read, and are interested in endurance and long term health and fitness, I HIGHLY recommend that book.